1. Field of the Invention
This invention relates to crosslinked wire and cable products. In one aspect the invention relates to a process for making crosslinked wire and cable products while in another aspect, the invention relates to a process for making crosslinked wire and cable products comprising a brominated flame retardant additive. In yet another aspect the invention relates to a process for making such products in one step.
2. Description of the Related Art
The Monosil process is a well known process (U.S. Pat. No. 4,117,195) for making crosslinked wire and cable products in a single step. In one typical embodiment, the process comprises metering into a screw extrusion machine polymer capable of being crosslinked by the use of hydrolysable unsaturated silane together with compounding ingredients comprising a hydrolysable unsaturated silane, a free-radical generator and a silanol condensation catalyst. These ingredients are blended with the polymer in the barrel of the extruder, and the temperature is raised sufficiently to effect grafting of silane groups to the polymer. The amount of free-radical generator is sufficiently low to limit direct free-radical crosslinking to a level that will not prevent extrusion of the material. The reaction mixture is extruded from the extruder through an extrusion die to form an elongate shaped product, e.g., a wire or cable sheath. While the product begins to experience crosslinking while still in the extruder, the cure is continued and completed outside the extruder by the action of moisture.
While this process is often the lowest cost process for making crosslinked extruded products, it is often difficult to conduct it in the presence of certain additives such as brominated flame retardant additives. If such additives are desired as part of the product, then these products are made in a two-step process (known as the Sioplas process) in which silane-grafted base polymer is prepared prior to the introduction of the brominated additive. This distracts from the process efficiency and thus adds cost to the products.